more than 400 cia strikes against targets in pakistan and yemen. eight times as many as under president bush. >> they have been very precise, precision strikes against al qaeda and their affiliates. >> these strikes are legal. they are ethical. and they are wise. >> reporter: but today, new questions about drone strikes targeting american citizens, including anwar al awlaki. born in new mexico and killed in yemen in 2011. he allegedly directed the so-called underwear bomber, who tried to blow up an airliner over detroit in 2009. but awlaki was never charged with a crime. nbc news has obtained this confidential 16-page justice department memo that concludes lethal strikes against u.s. citizens who are operational leaders of al qaeda are a lawful act of national self-defense. >> we only take these kinds of actions when there's an imminent threat, when capture is not feasible, and when we are confident that we're doing so in a way that's consistent with federal and international law. >> reporter: but the memo appears to allow greater leeway than the a